If it refers to advanced English for students who have learned English as a second or foreign language it means it is a course that will:
take for granted that the students have met most English grammar points
assume that they will need revision of these
introduce a variety of reading and listening tasks that help students to understand different styles of written and spoken English
give instruction and practice in producing a variety of different kinds of written text
develop students' vocabulary to help them cope with formal, highly colloquial or academic texts
Non native learners of English have different needs at different stages as their knowledge expands, so books are divided into levels, beginner, pre-intermediate, intermediate, upper intermediate, advanced.